When i changed my pulley last week i checked the vacuum T under the supercharge snout to have it crumble and break in two when i tried to pull it off to check for cracks. It appeared to have been cracked half way around where it attached to the LIM for who knows how long. I just picked up the T'* and vacuum hose setup from the dealer and replaced the vacuum line and T'* from the BCA (or is it the BCS?) to the fuel pressure regulator to the LIM. I took it out for a test drive and it feels like it just runs better, with a seat of the pants noticeable difference. Can having a vacuum leak take that much power?
As many here have found, a vacuum leak, even a "small" one, can make a very big difference in performance.
It can cause noticeable stutters and stumbles, poor gas mileage, bad idle, loss of power, and even occasional complete power loss upon hard braking or at stop signs. It depends somewhat on where the breaks in your line are.
I'm really impressed. When i first found the T cracked i tried to take it off only breaking it completely in two. I tried getting a replacement at autozone but the dorman ones were just to small. Unfortunately i had to tape the hell out of it with electrical tape and take it easy on it for the labor day weekend as the part departments weren't open. I went to change it last night and the vacuum T had completely come off the LIM so i don't even want to think about the amount of un metered air going in/out. I also am seeing less KR but im not sure if i should attribute that to putting my IAT closer to the filter using Wrens how to or the fact that i had a gaping vacuum leak.